Pesticide granules and method of preparing such granules

ABSTRACT

Pesticidal granules containing a volatile pesticide and a carrier containing a mineral which absorbs water only very slowly.

nited States Patent [72] Inventors Appl. No,

Priorities Werner Duyfjes Amsterdam;

Willem De Lange, Amsterdam; Johan Thomas Minnigh, Rotterdam, all ofNetherlands June 27, 1967 Nov. 2, 1971 U. S. Philips Corporation NewYork, N.Y.

June 28, 1966 Netherlands June 6, 1967, Netherlands, No. 6707830PESTICIDE GRANULES AND METHOD OF PREPARING SUCH GRANULES 3 Claims, NoDrawings 71/79, 7l/88 424/167, 71/DlG.1

[51] lnt.Cl A0ln 9/00 [50] Field of Search 7l/DlG. 1, 65, 105, 79

[56] References Cited UNITED STATES PATENTS 2,992,090 7/1961 Littler7l/D1G. 1 3,056,723 10/1962 Galloway... 71/D1G. 1 3,168,437 2/1965Galloway... 7l/D1G. 1 2,792,295 5/1957 Wright 71/DIG. l FOREIGN PATENTS589,926 12/1959 Canada 71/DlG. 1 1,519,731 2/1968 France 7l/D1G. 1

Primary Examiner-James 0. Thomas, Jr. Alt0rney- Frank R. TrifariABSTRACT: Pesticidal granules containing a volatile pesticide and acarrier containing a mineral which absorbs water only very slowly.

PESTICIDE GRANULES AND METHOD OF PREPARING SUCH GRANULES The inventionrelates to pesticide granules and to a method of preparing suchgranules.

In this application, the term pesticides is employed to signifycompositions used for combating harmful organisms in agriculture,horticulture or sylviculture such as insecticides, fungicides,herbicides, bactericides and nematicides.

These pesticides are generally processed to so-called miscible oils orwettable powders and, after dilution with water, sprayed or atomizedontothe vegetation. The pesticides may alternatively be processed toso-called dusts which are. dusted onto the vegetation. Especially inrecent years, a slightly modified form of processing, i.e. the so-calledgranular form, has come into prominence. The granular compositionconcerned is spread on the soil or in the water and disintegratesunderthe influence or without the influence of water. The. diameters of thesegrains may vary, for example, between 0.l mm. and 0.5 cm.

These grains are generally prepared by mixing an inert, mostlypulverulent mineral carrier material with a hinder, the pesticide andwater and, by then granulatingthe moist powder; thus obtained. The moistpowder may be granulated, for=example, by pressing it to plates, strips,tapes or tablets and the like and by then crumbling this material andsieving it. In order to expel undesired quantities of water, thegranulate must often be dried. This technique is generally referred toas,- compacting" technique.

According to a known method, a mixture of magnesium sulfate, clay,bentonite, lignin sulfonate and active pesticide-is ground and thenintroduced into a rotating disc-shaped "pelletiser." During rotation ofthe pellctizer, water up to a quantity This 25 percent is atomized ontothe mixture. Thus, grains. of a given size are obtained which solidifydue to the waterbinding properties of the magnesium sulfate. This methodis not always suitable in practice because of the comparatively highcost price of bentonite, and the necessity to remove water therefrom.

According to another method, marble, limestone or calcite havinga Mohshardness between 3 and 4 is crumbled to a grain size of 0.4 to 2 mm.,whereupon the grains are first wetted by spraying them with an aqueoussolution ofsurfaceactive substance and then coated with a compositionwhich beside a pesticide contains an inert carrier material, a binderand a surface-active substance.

According to another method, dry granular sodium borate and a solidgrandular herbicide sparingly soluble in water are mixed in the presenceof water, the water and the herbicide particles being absorbed at thesodium borate particles.

Although satisfactory results, are obtained with many. of. thesemethods, they are not always suitable in special cases, for example,when due to particular physical properties, the pesticide cannot beprocessed to stable granules by the said techniques. A specialdifficulty arises if the pesticide has-a comparatively high volatility.in the presence of water. When the temperature of the granule increases,part of the incorporated water will evaporate as a result of which alsopart of the. pesticide that can be distilled together with water willvolatilize. When the granules are stored, this. will give rise tomisgrowth of the granules in the packing owing to crystal growth of thepesticide on the surface of the granules so that the composition becomesunusual.

Investigations leading to the invention have shown that in practice thewater content of granules containing. av pesticide that can be distilledtogether with water is not permitted to exceed 5 percent by weight andispreferably lower than 2.5 percent.

In the methods of preparing granules which have beenused hitherto, thecontent of water was comparatively high, i.e. approximately 5 to 25percent by weight of the total granule weight. This often requiredeither the use of special substances for binding this quantity of water,for example gypsum which is capable of retaining the water in the formof crystal water, or the use of a drying process for expelling theundesired quantity of water. These processes both render the preparationof granulescomparatively expensive, while moreover pesticide is lost dueto its codistillation with water. Furthermore, for practical reasons, itis not possible to obtain by one of these methods a granule the readilyevaporable'water content of which lies below 5 percent of the granuleweight. Since these known techniques provide granules havingacomparatively high water content, they are-less suitable for processingto granules of pesticides which are volatile in.the presence of water.

The invention relates to granules of a special composition which containa pesticide which is volatile in the'presence of water. The inventionfurther relates to an improved method of preparing such granules withthe aid of. the compacting technique.

The granules according to the invention contain a small quantity ofwater, a pesticide volatile in the presence of water, a binder and aspecial carrier material. Due to a particular composition, the grainshave a high stability also for longstoring periods and the losses ofpesticide are comparatively small in these periods, while the disturbingformation of a cake of granulesis substantially completely avoided. Thegranules also have a high resistance, to wear.

A pesticide which is volatile in the presence of water is to beunderstood to mean hereinafter a pesticidethe steam distillationconstant of which is in excess of l. The manner in which thisconstantcan be determined has been described extensively in the literature ofthe analytic chemistry (cf. inter alia Schoorl, Organische Analyse,Amsterdam 1937, Volume, ll, pages to I97). Theoretically, the steamdistillation constant may become, infinitely large, but in practicethis; value rarely exceeds35. For 2,6-dichlorobenzonitrik; a known weedkiller, this value is 20.61037, as has beenfound by the applicant.

As examplesRof substances which are suitable for use in the methodaccording to the invention, the following pesticides can. be mentioned:2,o-dichlorobenzonitrile; 2,6-dichlorothiobenzamite;' pentachlorophenol;4chloropyridine; 5-(3,4-.dichlorophenyl)-l,- methoxyl -meth.ylurea;5-(4-chlorophenyl)- l -methoxy l methyl 3-amino-2,S-dichlorobenzoicacid; hexachlorocyclohexane, D.D.To; 4-trifluoromethyl-2,6-dinitro-N,N-dipropylaniline; S-n-propyl ethyI-Z-butyl-thiol carbamate; 8- ethyll-hexamethylene imine carbothiolate; 0,0'-dimethyl-O'cyclohexene-l-ylrphosphate and the corresponding; 0,0- diethyl compound;2-chloro-allyl-diethyl-dithio-carbamate; a -chloro-N,N-diallylacetamide; mixtures of l,2-dichloropropane and, l,3-dichloro-propene andof the corresponding dibromo-compounds;l-(chlor0-2-norbornyl)-3,3-dimethylurea; 4-chloro-pyridine N-oxyde.According to the invention. granules can be prepared which contain l to50 percent of pesticide.

The carrier material is characterized in that it satisfies the twofollowing; conditions:

1. A powder. ofithecarrier material having an average particle size of0.5 to 0.05 mm. is no longer "free flowing" with a water content of 2 to7 percent and readily agglomerates.

2. A mixture of the, carrier material, binder and pesticide whichhas awater-content of 2 to 7 percentand whichreadily, passes, into acrumblyphase of agglomerated particlescan be compressed to plates, strips,tapes or tablets all the surfaces of which have a substantially constanthardness. Due to. these properties, the pulverization of the plates,Strips, tapes or tablets when theyare crumbled to granules and processedis only slight andthe. granules have a high resistance to wear.

According to. the improved method of preparing these granules, by asuitable, choice, of carrier material, comparatively small quantities ofwater are sufficient to cause themixture of pesticide, carrier materialand binder to pass to the crumbled phase which is required to compressthe mixture to plates, strips, tapes or tablets of substantiallyconstant hardness. In this specific preparation method according totheinvention, a drying process becomes superfluous so that losses ofpesticide, which would occur owing to the volatility of pesticide in thepresent of water, can be avoided.

The carrier material according to the invention is characterized in thata mixture of a powder of this material and a binder is no longer "freeflowing" already with a water content of 2 to 7 percent and readilyforms a crumbly powder of agglomerated particles.

Carrier materials satisfying the said conditions are especially mineralsof the carbonate type such as calcium carbonate, magnesium carbonate orcalcium magnesium carbonate. Examples are dolomite, chalk, limestone,marl or marble or mixtures thereof. Satisfactory results were obtainedmore particularly with dolomite.

However, as an alternative strong water-binding carrier materials may beused, for example silicates, amongst other kaolinite attapulgite,bentonite, anhydrous calcium sulfate which have been treated with awater-repellent agent such as a fatty alcohol, a silicon oil, ahydrocarbon oil or a higher fatty acid such as stearic acid, as a resultof which separate particles are surrounded by a layer of water-repellentagent, due to which water is less rapidly absorbed.

In other words, use is generally made of powdered minerals which take upwater, either slowly or to a low percentage, and which have theseproperties either by nature or by a special step. The carrier materialsto be used in accordance with the invention which satisfy the aboveconditions are referred to hereinafter as water-repellent mineralpowders.

Thus, the invention relates to pesticide granules which contain beside apesticide a carrier material, a binder and water and which arecharacterized in that the pesticide is volatile in the presence ofwater, in that the carrier material is a powdered mineral which take upmineral either slowly or to a low percentage and in that the watercontent does not exceed 5 percent by weight. The invention furtherrelates to the following method of preparing said granules: a crumblymixture of pesticide, a powdered mineral as hereinbefore indicated, abinder and 2 to 7 percent of water is compressed to plates, strips,tapes or tablets which are then crumbled to granules of the desireddimensions. .The binder serves to ensure not only that the constituentsto be mixed firmly adhere to each other under the influence ofwater andunder pressure, but also that the granules, when they have been spreadon the soil or in the water, disintegrate under the influence of waterso that the pesticide can become effective. Therefore, it is notnecessary for the binder to be completely soluble in water. Stronglyvarying kinds of suitable hydrophilic binders can be mentioned, such asalbumins or carbohydrates, and further binders on the basis of syntheticresin, such as sodium-, or calcium caseinate, gelatin, skim or wholemilk powder, alginates, pectinates, starch hydrolisates,polysaccharides, acrylates, lignin sulfonates, sodium silicate andpolyvinyl pyrrolidon or polyethylene polysulfide. In practice, calciumlignin sulfonate has proved particularly suitable for use in the methodaccording to the invention. The commercial product is generally a moreor less purified product which has been obtained by the decomposition ofwood by means of calcium bisulfite. Calcium lignin sulfonate is alsoknown under the name of sulfite lye.

In order to obtain satisfactory granules, it is desirable that thequantity of binder should be 1 to 10 percent of the total granuleweight.

A crumbly mixture of pesticide, carrier material, binder and water canbe obtained by a conventional method. in a very suitable method, finelyground carrier material, pesticide and binder are mixed without previousaddition of water and this mixture is sprayed in a rotating drum with 2to 7 percent by weight of water. This water may contain a binder. Duringthis treatment, the mixture loses its powdered structure and theseparate particles are united in a more or less loose cohesion tocomparatively coarse soft grains so that the original "free flowing"mixture passes to a crumbled phase.

In a slightly modified method, the starting mixture consists ofpesticide, carrier material, binder and, as the case may be,

other auxiliary substances which already contain to a lesser or greaterextent the desired quantity of water, so that no water at all or only asmaller quantity of water need be added. In general, the manner in whichthe total content of water of 2 to 7 percent of the mixture to becompressed is attained, is not essential. ln this respect, it is solelyof importance that the mixture to be pressed should be in a crumbledstate. it is further recommendable that the particle size of theconstituents to be mixed should be small and should lie, for example,between 0.001 and 1 mm. In general, a suitable average particle sizeofthe pesticide lies between 0.00l and 0.5 mm. A suitable particle sizefor a pesticide satisfactorily soluble in water lies between 0.2 and 0.5mm., while for a pesticide sparingly soluble in water a particle size of0.00l to 0.02 mm. is more satisfactory. The particle size of the mineralpowder is preferably smaller than 0.5 mm. Satisfactory results wereobtained with a mineral powder having example, average particle size of0.1 to 0.2 mm. It is generally recommendable that the particle size ofthe carrier material should exceed a few times, for example, by a factor10, that of the pesticide.

if desired, surface-active substance or a conditioner is added to thebinder or to the remaining constituents. Thus, it is ensured that thebinder contacts more uniformly both the particles of the carrier andthose of the pesticide.

Suitable surface-active substances are sulfated fatty alcohols,alkylaryl sulfonates, alkylphenol polyglycol ethers, fatty acid N-alkyltaurates. lt is also advantageous to use in this compositioncation-active surface-active substances such as cetyltrimethylammoniumchloride or other quaternary ammonium compounds. Conditioners producingthe desired effeet are especially silicon compounds, more particularlycolloidal silicon dioxide, precipitated or nonprecipitated silicates,for example, calcium silicates.

According to the invention, satisfactory granules can also be preparedwithout the use of these surface-active substances or conditioners, butif these substances are used, the quantity of surface-active substanceand/or conditioner suitably lies between 0 and 5 percent.

Furthermore, it may be recommendable to add specific binders to improvethe hardness of the granules. Sodium metasilicate has provedparticularly suitable to obtain a hard granule.

The use of these substances is not essential either to obtain thegranules in accordance with the invention. If these substances are used,however, a quantity of 0 to 5 percent by weight is sufficient.

When the crumbly mixture is pressed, for example, by passing it betweentwo rotating rollers, plates, strips, tapes or tablets can be obtainedwhich, after being crumbled and granulated, are processed to granules.in general, the pressure applied is at least 300 kg./sq.cm. preferablyabove 500 kg./sq.cm. Due to the exerted pressure, the temperatureincreases so that part of the water in the mixture evaporates, as aresult of which the content of water in the final product can be readilyreduced to a value below 4 percent. By a suitable choice of thequantities of carrier material, binder, active substance and water, thewhole process can be carried out so that the final product does notcontain more than I to 2.5 percent of water.

The mass pressed to plates, strips, tapes or tablets can be processed togranules by any suitable method. in one of the simplest methods, thecompressed mass is crumbled in a crumbler to small particles. With theaid of these crumblers, a comparatively high percentage of particleshaving a size of 0.25 to L25 mm. can be obtained, which particles canthen be separated by sieving. The part of the granulate the particles ofwhichare considered to be too small or too large, can be readily fedback into the processing.

The granular composition according to the invention preferably contains1 to 50 percent by weight of a pesticide having a steam distillationconstant in excess of l, l to 10 percent by weight ofa binder of thekind described above. I to 4 percent by weight of water, 0 to 5 percentby weight of surface-active substance and 0 to 5 percent by weight ofasolidifying agent and/or of a conditioner, and for the remaining part amineral powder mainly consisting of calcium, magnesiumor magnesiumcalcium carbonate and its grains have an average cross section of 0.25to l mm.

The invention is of particular advantage for granulating 2,6-dichlorobenzonitrile. A granule thus prepared in accordance with theinvention preferably has the following composition: 2 to ID percent byweight of 2,6-dichlorobenzonitrile, 4 to 10 percent by weight of calciumlignin sulfonate (dry weight), to 2 percent by weight of a wettingagent, 1 to 2.5 percent by weight of water and for the remaining partdolomite or marl, the average particle size of the granulate lyingbetween 0.25 and 1.25 mm.

EXAMPLE Eighty-four Kg. of ground dolomite (or marl), 5 kg. of powderedsulfite lye, l kg. of sodium salt of sulfated fatty alcohols, and I0 kg.of ground 2,6-dichlorobenzonitrile (99 percent of the particles have asize smaller than 44 1.) were mixed in a horizontally arranged mixer.After complete homogenization of the mixture, 2 liters of water areatomized onto the powder while stirring, whereupon an after-mixingtreatment is carried out for a few minutes.

The powder, which has been wetted with water and has become crumbly, isnow introduced into a socalled "compactor" which compresses the powderunder high pressure (6,000 kg./sq.cm.) to tapes," strips," plates" ortablets."

Heat is developed during this process so that part of the waterevaporates.

The strips, tapes", plates" or "tablets" are very hard after cooling andare then passed through a crumbler which crumbles a major part of thestrips to granules.

These granules are separated by a continuously operating sieving machinein the desired sizes.

The unduly fine (pulverulent) part is fed back into the mixing apparatusand the unduly coarse part is crumbled again by the crumbler, thegranules being again separated in the desired sizes by the sievingmachine. The granulate thus obtained contained 2 percent by weight ofwater and had an average particle size of 0.75 mm.

What is claimed is:

1. A method of preparing pesticidal granules comprising a pesticidehaving a steam distillation constant in excess of l in a pesticidallyeffective amount, a binder, a carrier material consisting essentially ofpowdered carbonates and water up to 5 percent by weight of thecomposition said method comprising preparing a crumbly mixture of thesolid ingredients involved including 2 to 7 percent of water, pressingsaid mixture into flat pieces and then crumbling said flat pieces intosmall particles.

2. The method of claim 1 wherein the water is introduced into thecrumbly mixture while mixing of the ingredients is carried on.

3. Pesticidal granules prepared according to the method of claim I.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,617,246 (mm 3.737) Dated November 2, 1971 Inventor(8) WERNER DUYFJESET AL It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

r- Column 2, line 33, "dichlorobenzonitrik" should bedichlorobenzonitrile line 43, D.D.to" should be D.D.T.

Signed and sealed this 11th day of July 1972.

(SEAL) Atte st:

EDWARD M.FL1L'ICHI1II, JR ROBERT GOITSCi-IALK Attesting Officer-Commissioner oi Patents

2. The method of claim 1 wherein the water is introduced into thecrumbly mixture while mixing of the ingredients is carried on. 3.Pesticidal granules prepared according to the method of claim